Bio unit 2

Animals use courtship behaviour as part of sexual reproduction. Courtship behaviour is innate, in other words it is genetically programmed, so all members of the same species show exactly the same courtship behaviour, while members of different species show different behaviours. Courtship behaviour can thus be used to identify individuals as members of the same or different species.

Courtship behaviour allows animals to:

Recognise members of their own species. This is particularly important where many very similar species live in the same habitat. Reproduction between members of different species may be possible, but won’t lead to fertile offspring, so should be avoided.

Attract a mate of the opposite sex.

Identify a mate that is capable of breeding. Both partners need to be sexually mature, fertile and receptive to mating. Many females only produce eggs at specific times, often just once a year.

Synchronise the production of eggs and sperm.

Form a pair bond and help raise the offspring.

Females will only mate with males showing the correct pattern of flashes and flight, ensuring mating only takes place between members of the same species. The flashing and flight patterns in males are entirely genetically-determined

It’s not possible to look at a whole species, so we usually investigate populations – the members of a species living in a particular area (e.g. the elm trees in the UK; the freshwater shrimps in a river; the woodlice in a churchyard), and only measure a sample of that population. The sample must be chosen carefully:

It must be a random sample, to avoid sample bias, such as accidentally (or deliberately) picking all the tallest individuals. For human samples we can give all the available individuals a number then use random numbers to pick the sample. For animals we can use a random trapping technique, and for plants (and stationary animals) we can place quadrats on the ground using random numbers to generate

coordinates.

It must be a large sample, to minimise the chance of picking a skewed sample and to allow for bad measurements or anomalies. The sample size is often called n. How big should n be? This depends on the measurements, but in general n should never be less than 10, and of possible it should be at least

100 or 1000.

As we’ve seen, genetic diversity means the number of different alleles present within a species. Genetic diversity is important because it is the basis of evolution and survival of a species. A species with a high genetic diversity is likely to have some individuals with the characteristics required to survive a change in the environment, so some members of the species will survive. Low genetic diversity means a species is

more likely to become extinct due to environmental changes.

Genetic Bottlenecks

A genetic bottleneck happens when a population is drastically reduced in size due to a natural catastrophe or a continual more gradual change in the environment. The few…